2 Stockfish, a UCI chess playing engine derived from Glaurung 2.1
3 Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
4 Copyright (C) 2008-2010 Marco Costalba, Joona Kiiski, Tord Romstad
6 Stockfish is free software: you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation, either version 3 of the License, or
9 (at your option) any later version.
11 Stockfish is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with this program. If not, see <http://www.gnu.org/licenses/>.
44 #include "ucioption.h"
50 //// Local definitions
56 enum NodeType { NonPV, PV };
58 // Set to true to force running with one thread.
59 // Used for debugging SMP code.
60 const bool FakeSplit = false;
62 // ThreadsManager class is used to handle all the threads related stuff in search,
63 // init, starting, parking and, the most important, launching a slave thread at a
64 // split point are what this class does. All the access to shared thread data is
65 // done through this class, so that we avoid using global variables instead.
67 class ThreadsManager {
68 /* As long as the single ThreadsManager object is defined as a global we don't
69 need to explicitly initialize to zero its data members because variables with
70 static storage duration are automatically set to zero before enter main()
76 int active_threads() const { return ActiveThreads; }
77 void set_active_threads(int newActiveThreads) { ActiveThreads = newActiveThreads; }
78 void incrementNodeCounter(int threadID) { threads[threadID].nodes++; }
79 void incrementBetaCounter(Color us, Depth d, int threadID) { threads[threadID].betaCutOffs[us] += unsigned(d); }
81 void resetNodeCounters();
82 void resetBetaCounters();
83 int64_t nodes_searched() const;
84 void get_beta_counters(Color us, int64_t& our, int64_t& their) const;
85 bool available_thread_exists(int master) const;
86 bool thread_is_available(int slave, int master) const;
87 bool thread_should_stop(int threadID) const;
88 void wake_sleeping_threads();
89 void put_threads_to_sleep();
90 void idle_loop(int threadID, SplitPoint* sp);
93 void split(const Position& pos, SearchStack* ss, int ply, Value* alpha, const Value beta, Value* bestValue,
94 Depth depth, Move threatMove, bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode);
100 volatile bool AllThreadsShouldExit, AllThreadsShouldSleep;
101 Thread threads[MAX_THREADS];
103 Lock MPLock, WaitLock;
105 #if !defined(_MSC_VER)
106 pthread_cond_t WaitCond;
108 HANDLE SitIdleEvent[MAX_THREADS];
114 // RootMove struct is used for moves at the root at the tree. For each
115 // root move, we store a score, a node count, and a PV (really a refutation
116 // in the case of moves which fail low).
120 RootMove() { nodes = cumulativeNodes = ourBeta = theirBeta = 0ULL; }
122 // RootMove::operator<() is the comparison function used when
123 // sorting the moves. A move m1 is considered to be better
124 // than a move m2 if it has a higher score, or if the moves
125 // have equal score but m1 has the higher beta cut-off count.
126 bool operator<(const RootMove& m) const {
128 return score != m.score ? score < m.score : theirBeta <= m.theirBeta;
133 int64_t nodes, cumulativeNodes, ourBeta, theirBeta;
134 Move pv[PLY_MAX_PLUS_2];
138 // The RootMoveList class is essentially an array of RootMove objects, with
139 // a handful of methods for accessing the data in the individual moves.
144 RootMoveList(Position& pos, Move searchMoves[]);
146 int move_count() const { return count; }
147 Move get_move(int moveNum) const { return moves[moveNum].move; }
148 Value get_move_score(int moveNum) const { return moves[moveNum].score; }
149 void set_move_score(int moveNum, Value score) { moves[moveNum].score = score; }
150 Move get_move_pv(int moveNum, int i) const { return moves[moveNum].pv[i]; }
151 int64_t get_move_cumulative_nodes(int moveNum) const { return moves[moveNum].cumulativeNodes; }
153 void set_move_nodes(int moveNum, int64_t nodes);
154 void set_beta_counters(int moveNum, int64_t our, int64_t their);
155 void set_move_pv(int moveNum, const Move pv[]);
157 void sort_multipv(int n);
160 static const int MaxRootMoves = 500;
161 RootMove moves[MaxRootMoves];
170 // Maximum depth for razoring
171 const Depth RazorDepth = 4 * OnePly;
173 // Dynamic razoring margin based on depth
174 inline Value razor_margin(Depth d) { return Value(0x200 + 0x10 * int(d)); }
176 // Step 8. Null move search with verification search
178 // Null move margin. A null move search will not be done if the static
179 // evaluation of the position is more than NullMoveMargin below beta.
180 const Value NullMoveMargin = Value(0x200);
182 // Maximum depth for use of dynamic threat detection when null move fails low
183 const Depth ThreatDepth = 5 * OnePly;
185 // Step 9. Internal iterative deepening
187 // Minimum depth for use of internal iterative deepening
188 const Depth IIDDepth[2] = { 8 * OnePly /* non-PV */, 5 * OnePly /* PV */};
190 // At Non-PV nodes we do an internal iterative deepening search
191 // when the static evaluation is bigger then beta - IIDMargin.
192 const Value IIDMargin = Value(0x100);
194 // Step 11. Decide the new search depth
196 // Extensions. Configurable UCI options
197 // Array index 0 is used at non-PV nodes, index 1 at PV nodes.
198 Depth CheckExtension[2], SingleEvasionExtension[2], PawnPushTo7thExtension[2];
199 Depth PassedPawnExtension[2], PawnEndgameExtension[2], MateThreatExtension[2];
201 // Minimum depth for use of singular extension
202 const Depth SingularExtensionDepth[2] = { 7 * OnePly /* non-PV */, 6 * OnePly /* PV */};
204 // If the TT move is at least SingularExtensionMargin better then the
205 // remaining ones we will extend it.
206 const Value SingularExtensionMargin = Value(0x20);
208 // Step 12. Futility pruning
210 // Futility margin for quiescence search
211 const Value FutilityMarginQS = Value(0x80);
213 // Futility lookup tables (initialized at startup) and their getter functions
214 int32_t FutilityMarginsMatrix[16][64]; // [depth][moveNumber]
215 int FutilityMoveCountArray[32]; // [depth]
217 inline Value futility_margin(Depth d, int mn) { return Value(d < 7 * OnePly ? FutilityMarginsMatrix[Max(d, 1)][Min(mn, 63)] : 2 * VALUE_INFINITE); }
218 inline int futility_move_count(Depth d) { return d < 16 * OnePly ? FutilityMoveCountArray[d] : 512; }
220 // Step 14. Reduced search
222 // Reduction lookup tables (initialized at startup) and their getter functions
223 int8_t ReductionMatrix[2][64][64]; // [pv][depth][moveNumber]
225 template <NodeType PV>
226 inline Depth reduction(Depth d, int mn) { return (Depth) ReductionMatrix[PV][Min(d / 2, 63)][Min(mn, 63)]; }
228 // Common adjustments
230 // Search depth at iteration 1
231 const Depth InitialDepth = OnePly;
233 // Easy move margin. An easy move candidate must be at least this much
234 // better than the second best move.
235 const Value EasyMoveMargin = Value(0x200);
243 // Scores and number of times the best move changed for each iteration
244 Value ValueByIteration[PLY_MAX_PLUS_2];
245 int BestMoveChangesByIteration[PLY_MAX_PLUS_2];
247 // Search window management
253 // Time managment variables
254 int SearchStartTime, MaxNodes, MaxDepth, ExactMaxTime;
255 bool UseTimeManagement, InfiniteSearch, PonderSearch, StopOnPonderhit;
256 bool FirstRootMove, AbortSearch, Quit, AspirationFailLow;
261 std::ofstream LogFile;
263 // Multi-threads related variables
264 Depth MinimumSplitDepth;
265 int MaxThreadsPerSplitPoint;
266 ThreadsManager ThreadsMgr;
268 // Node counters, used only by thread[0] but try to keep in different cache
269 // lines (64 bytes each) from the heavy multi-thread read accessed variables.
271 int NodesBetweenPolls = 30000;
278 Value id_loop(const Position& pos, Move searchMoves[]);
279 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr);
281 template <NodeType PvNode>
282 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
284 template <NodeType PvNode>
285 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply);
287 template <NodeType PvNode>
288 void sp_search(SplitPoint* sp, int threadID);
290 template <NodeType PvNode>
291 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck, bool singleEvasion, bool mateThreat, bool* dangerous);
293 bool connected_moves(const Position& pos, Move m1, Move m2);
294 bool value_is_mate(Value value);
295 Value value_to_tt(Value v, int ply);
296 Value value_from_tt(Value v, int ply);
297 bool move_is_killer(Move m, SearchStack* ss);
298 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply);
299 bool connected_threat(const Position& pos, Move m, Move threat);
300 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply);
301 void update_history(const Position& pos, Move move, Depth depth, Move movesSearched[], int moveCount);
302 void update_killers(Move m, SearchStack* ss);
303 void update_gains(const Position& pos, Move move, Value before, Value after);
305 int current_search_time();
306 std::string value_to_uci(Value v);
310 void wait_for_stop_or_ponderhit();
311 void init_ss_array(SearchStack* ss, int size);
312 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value);
313 void insert_pv_in_tt(const Position& pos, Move pv[]);
314 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]);
316 #if !defined(_MSC_VER)
317 void *init_thread(void *threadID);
319 DWORD WINAPI init_thread(LPVOID threadID);
329 /// init_threads(), exit_threads() and nodes_searched() are helpers to
330 /// give accessibility to some TM methods from outside of current file.
332 void init_threads() { ThreadsMgr.init_threads(); }
333 void exit_threads() { ThreadsMgr.exit_threads(); }
334 int64_t nodes_searched() { return ThreadsMgr.nodes_searched(); }
337 /// init_search() is called during startup. It initializes various lookup tables
341 int d; // depth (OnePly == 2)
342 int hd; // half depth (OnePly == 1)
345 // Init reductions array
346 for (hd = 1; hd < 64; hd++) for (mc = 1; mc < 64; mc++)
348 double pvRed = 0.33 + log(double(hd)) * log(double(mc)) / 4.5;
349 double nonPVRed = 0.33 + log(double(hd)) * log(double(mc)) / 2.25;
350 ReductionMatrix[PV][hd][mc] = (int8_t) ( pvRed >= 1.0 ? floor( pvRed * int(OnePly)) : 0);
351 ReductionMatrix[NonPV][hd][mc] = (int8_t) (nonPVRed >= 1.0 ? floor(nonPVRed * int(OnePly)) : 0);
354 // Init futility margins array
355 for (d = 1; d < 16; d++) for (mc = 0; mc < 64; mc++)
356 FutilityMarginsMatrix[d][mc] = 112 * int(log(double(d * d) / 2) / log(2.0) + 1.001) - 8 * mc + 45;
358 // Init futility move count array
359 for (d = 0; d < 32; d++)
360 FutilityMoveCountArray[d] = 3 + (1 << (3 * d / 8));
364 /// perft() is our utility to verify move generation is bug free. All the legal
365 /// moves up to given depth are generated and counted and the sum returned.
367 int perft(Position& pos, Depth depth)
369 MoveStack mlist[256];
374 // Generate all legal moves
375 MoveStack* last = generate_moves(pos, mlist);
377 // If we are at the last ply we don't need to do and undo
378 // the moves, just to count them.
380 return int(last - mlist);
382 // Loop through all legal moves
384 for (MoveStack* cur = mlist; cur != last; cur++)
387 pos.do_move(m, st, ci, pos.move_is_check(m, ci));
388 sum += perft(pos, depth - OnePly);
395 /// think() is the external interface to Stockfish's search, and is called when
396 /// the program receives the UCI 'go' command. It initializes various
397 /// search-related global variables, and calls root_search(). It returns false
398 /// when a quit command is received during the search.
400 bool think(const Position& pos, bool infinite, bool ponder, int time[], int increment[],
401 int movesToGo, int maxDepth, int maxNodes, int maxTime, Move searchMoves[]) {
403 // Initialize global search variables
404 StopOnPonderhit = AbortSearch = Quit = AspirationFailLow = false;
406 ThreadsMgr.resetNodeCounters();
407 SearchStartTime = get_system_time();
408 ExactMaxTime = maxTime;
411 InfiniteSearch = infinite;
412 PonderSearch = ponder;
413 UseTimeManagement = !ExactMaxTime && !MaxDepth && !MaxNodes && !InfiniteSearch;
415 // Look for a book move, only during games, not tests
416 if (UseTimeManagement && get_option_value_bool("OwnBook"))
418 if (get_option_value_string("Book File") != OpeningBook.file_name())
419 OpeningBook.open(get_option_value_string("Book File"));
421 Move bookMove = OpeningBook.get_move(pos, get_option_value_bool("Best Book Move"));
422 if (bookMove != MOVE_NONE)
425 wait_for_stop_or_ponderhit();
427 cout << "bestmove " << bookMove << endl;
432 // Read UCI option values
433 TT.set_size(get_option_value_int("Hash"));
434 if (button_was_pressed("Clear Hash"))
437 CheckExtension[1] = Depth(get_option_value_int("Check Extension (PV nodes)"));
438 CheckExtension[0] = Depth(get_option_value_int("Check Extension (non-PV nodes)"));
439 SingleEvasionExtension[1] = Depth(get_option_value_int("Single Evasion Extension (PV nodes)"));
440 SingleEvasionExtension[0] = Depth(get_option_value_int("Single Evasion Extension (non-PV nodes)"));
441 PawnPushTo7thExtension[1] = Depth(get_option_value_int("Pawn Push to 7th Extension (PV nodes)"));
442 PawnPushTo7thExtension[0] = Depth(get_option_value_int("Pawn Push to 7th Extension (non-PV nodes)"));
443 PassedPawnExtension[1] = Depth(get_option_value_int("Passed Pawn Extension (PV nodes)"));
444 PassedPawnExtension[0] = Depth(get_option_value_int("Passed Pawn Extension (non-PV nodes)"));
445 PawnEndgameExtension[1] = Depth(get_option_value_int("Pawn Endgame Extension (PV nodes)"));
446 PawnEndgameExtension[0] = Depth(get_option_value_int("Pawn Endgame Extension (non-PV nodes)"));
447 MateThreatExtension[1] = Depth(get_option_value_int("Mate Threat Extension (PV nodes)"));
448 MateThreatExtension[0] = Depth(get_option_value_int("Mate Threat Extension (non-PV nodes)"));
450 MinimumSplitDepth = get_option_value_int("Minimum Split Depth") * OnePly;
451 MaxThreadsPerSplitPoint = get_option_value_int("Maximum Number of Threads per Split Point");
452 MultiPV = get_option_value_int("MultiPV");
453 Chess960 = get_option_value_bool("UCI_Chess960");
454 UseLogFile = get_option_value_bool("Use Search Log");
457 LogFile.open(get_option_value_string("Search Log Filename").c_str(), std::ios::out | std::ios::app);
459 read_weights(pos.side_to_move());
461 // Set the number of active threads
462 int newActiveThreads = get_option_value_int("Threads");
463 if (newActiveThreads != ThreadsMgr.active_threads())
465 ThreadsMgr.set_active_threads(newActiveThreads);
466 init_eval(ThreadsMgr.active_threads());
469 // Wake up sleeping threads
470 ThreadsMgr.wake_sleeping_threads();
473 int myTime = time[pos.side_to_move()];
474 int myIncrement = increment[pos.side_to_move()];
475 if (UseTimeManagement)
476 TimeMgr.init(myTime, myIncrement, movesToGo, pos.startpos_ply_counter());
478 // Set best NodesBetweenPolls interval to avoid lagging under
479 // heavy time pressure.
481 NodesBetweenPolls = Min(MaxNodes, 30000);
482 else if (myTime && myTime < 1000)
483 NodesBetweenPolls = 1000;
484 else if (myTime && myTime < 5000)
485 NodesBetweenPolls = 5000;
487 NodesBetweenPolls = 30000;
489 // Write search information to log file
491 LogFile << "Searching: " << pos.to_fen() << endl
492 << "infinite: " << infinite
493 << " ponder: " << ponder
494 << " time: " << myTime
495 << " increment: " << myIncrement
496 << " moves to go: " << movesToGo << endl;
498 // We're ready to start thinking. Call the iterative deepening loop function
499 id_loop(pos, searchMoves);
504 ThreadsMgr.put_threads_to_sleep();
512 // id_loop() is the main iterative deepening loop. It calls root_search
513 // repeatedly with increasing depth until the allocated thinking time has
514 // been consumed, the user stops the search, or the maximum search depth is
517 Value id_loop(const Position& pos, Move searchMoves[]) {
519 Position p(pos, pos.thread());
520 SearchStack ss[PLY_MAX_PLUS_2];
521 Move pv[PLY_MAX_PLUS_2];
522 Move EasyMove = MOVE_NONE;
523 Value value, alpha = -VALUE_INFINITE, beta = VALUE_INFINITE;
525 // Moves to search are verified, copied, scored and sorted
526 RootMoveList rml(p, searchMoves);
528 // Handle special case of searching on a mate/stale position
529 if (rml.move_count() == 0)
532 wait_for_stop_or_ponderhit();
534 return pos.is_check() ? -VALUE_MATE : VALUE_DRAW;
537 // Print RootMoveList startup scoring to the standard output,
538 // so to output information also for iteration 1.
539 cout << "info depth " << 1
540 << "\ninfo depth " << 1
541 << " score " << value_to_uci(rml.get_move_score(0))
542 << " time " << current_search_time()
543 << " nodes " << ThreadsMgr.nodes_searched()
545 << " pv " << rml.get_move(0) << "\n";
550 init_ss_array(ss, PLY_MAX_PLUS_2);
551 pv[0] = pv[1] = MOVE_NONE;
552 ValueByIteration[1] = rml.get_move_score(0);
555 // Is one move significantly better than others after initial scoring ?
556 if ( rml.move_count() == 1
557 || rml.get_move_score(0) > rml.get_move_score(1) + EasyMoveMargin)
558 EasyMove = rml.get_move(0);
560 // Iterative deepening loop
561 while (Iteration < PLY_MAX)
563 // Initialize iteration
565 BestMoveChangesByIteration[Iteration] = 0;
567 cout << "info depth " << Iteration << endl;
569 // Calculate dynamic aspiration window based on previous iterations
570 if (MultiPV == 1 && Iteration >= 6 && abs(ValueByIteration[Iteration - 1]) < VALUE_KNOWN_WIN)
572 int prevDelta1 = ValueByIteration[Iteration - 1] - ValueByIteration[Iteration - 2];
573 int prevDelta2 = ValueByIteration[Iteration - 2] - ValueByIteration[Iteration - 3];
575 AspirationDelta = Max(abs(prevDelta1) + abs(prevDelta2) / 2, 16);
576 AspirationDelta = (AspirationDelta + 7) / 8 * 8; // Round to match grainSize
578 alpha = Max(ValueByIteration[Iteration - 1] - AspirationDelta, -VALUE_INFINITE);
579 beta = Min(ValueByIteration[Iteration - 1] + AspirationDelta, VALUE_INFINITE);
582 // Search to the current depth, rml is updated and sorted, alpha and beta could change
583 value = root_search(p, ss, pv, rml, &alpha, &beta);
585 // Write PV to transposition table, in case the relevant entries have
586 // been overwritten during the search.
587 insert_pv_in_tt(p, pv);
590 break; // Value cannot be trusted. Break out immediately!
592 //Save info about search result
593 ValueByIteration[Iteration] = value;
595 // Drop the easy move if differs from the new best move
596 if (pv[0] != EasyMove)
597 EasyMove = MOVE_NONE;
599 if (UseTimeManagement)
602 bool stopSearch = false;
604 // Stop search early if there is only a single legal move,
605 // we search up to Iteration 6 anyway to get a proper score.
606 if (Iteration >= 6 && rml.move_count() == 1)
609 // Stop search early when the last two iterations returned a mate score
611 && abs(ValueByIteration[Iteration]) >= abs(VALUE_MATE) - 100
612 && abs(ValueByIteration[Iteration-1]) >= abs(VALUE_MATE) - 100)
615 // Stop search early if one move seems to be much better than the others
616 int64_t nodes = ThreadsMgr.nodes_searched();
619 && ( ( rml.get_move_cumulative_nodes(0) > (nodes * 85) / 100
620 && current_search_time() > TimeMgr.available_time() / 16)
621 ||( rml.get_move_cumulative_nodes(0) > (nodes * 98) / 100
622 && current_search_time() > TimeMgr.available_time() / 32)))
625 // Add some extra time if the best move has changed during the last two iterations
626 if (Iteration > 5 && Iteration <= 50)
627 TimeMgr.pv_unstability(BestMoveChangesByIteration[Iteration],
628 BestMoveChangesByIteration[Iteration-1]);
630 // Stop search if most of MaxSearchTime is consumed at the end of the
631 // iteration. We probably don't have enough time to search the first
632 // move at the next iteration anyway.
633 if (current_search_time() > (TimeMgr.available_time() * 80) / 128)
639 StopOnPonderhit = true;
645 if (MaxDepth && Iteration >= MaxDepth)
649 // If we are pondering or in infinite search, we shouldn't print the
650 // best move before we are told to do so.
651 if (!AbortSearch && (PonderSearch || InfiniteSearch))
652 wait_for_stop_or_ponderhit();
654 // Print final search statistics
655 cout << "info nodes " << ThreadsMgr.nodes_searched()
657 << " time " << current_search_time() << endl;
659 // Print the best move and the ponder move to the standard output
660 if (pv[0] == MOVE_NONE)
662 pv[0] = rml.get_move(0);
666 assert(pv[0] != MOVE_NONE);
668 cout << "bestmove " << pv[0];
670 if (pv[1] != MOVE_NONE)
671 cout << " ponder " << pv[1];
678 dbg_print_mean(LogFile);
680 if (dbg_show_hit_rate)
681 dbg_print_hit_rate(LogFile);
683 LogFile << "\nNodes: " << ThreadsMgr.nodes_searched()
684 << "\nNodes/second: " << nps()
685 << "\nBest move: " << move_to_san(p, pv[0]);
688 p.do_move(pv[0], st);
689 LogFile << "\nPonder move: "
690 << move_to_san(p, pv[1]) // Works also with MOVE_NONE
693 return rml.get_move_score(0);
697 // root_search() is the function which searches the root node. It is
698 // similar to search_pv except that it uses a different move ordering
699 // scheme, prints some information to the standard output and handles
700 // the fail low/high loops.
702 Value root_search(Position& pos, SearchStack* ss, Move* pv, RootMoveList& rml, Value* alphaPtr, Value* betaPtr) {
709 Depth depth, ext, newDepth;
710 Value value, alpha, beta;
711 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
712 int researchCountFH, researchCountFL;
714 researchCountFH = researchCountFL = 0;
717 isCheck = pos.is_check();
718 depth = (Iteration - 2) * OnePly + InitialDepth;
720 // Step 1. Initialize node (polling is omitted at root)
721 ss->currentMove = ss->bestMove = MOVE_NONE;
723 // Step 2. Check for aborted search (omitted at root)
724 // Step 3. Mate distance pruning (omitted at root)
725 // Step 4. Transposition table lookup (omitted at root)
727 // Step 5. Evaluate the position statically
728 // At root we do this only to get reference value for child nodes
729 ss->eval = isCheck ? VALUE_NONE : evaluate(pos, ei);
731 // Step 6. Razoring (omitted at root)
732 // Step 7. Static null move pruning (omitted at root)
733 // Step 8. Null move search with verification search (omitted at root)
734 // Step 9. Internal iterative deepening (omitted at root)
736 // Step extra. Fail low loop
737 // We start with small aspiration window and in case of fail low, we research
738 // with bigger window until we are not failing low anymore.
741 // Sort the moves before to (re)search
744 // Step 10. Loop through all moves in the root move list
745 for (int i = 0; i < rml.move_count() && !AbortSearch; i++)
747 // This is used by time management
748 FirstRootMove = (i == 0);
750 // Save the current node count before the move is searched
751 nodes = ThreadsMgr.nodes_searched();
753 // Reset beta cut-off counters
754 ThreadsMgr.resetBetaCounters();
756 // Pick the next root move, and print the move and the move number to
757 // the standard output.
758 move = ss->currentMove = rml.get_move(i);
760 if (current_search_time() >= 1000)
761 cout << "info currmove " << move
762 << " currmovenumber " << i + 1 << endl;
764 moveIsCheck = pos.move_is_check(move);
765 captureOrPromotion = pos.move_is_capture_or_promotion(move);
767 // Step 11. Decide the new search depth
768 ext = extension<PV>(pos, move, captureOrPromotion, moveIsCheck, false, false, &dangerous);
769 newDepth = depth + ext;
771 // Step 12. Futility pruning (omitted at root)
773 // Step extra. Fail high loop
774 // If move fails high, we research with bigger window until we are not failing
776 value = - VALUE_INFINITE;
780 // Step 13. Make the move
781 pos.do_move(move, st, ci, moveIsCheck);
783 // Step extra. pv search
784 // We do pv search for first moves (i < MultiPV)
785 // and for fail high research (value > alpha)
786 if (i < MultiPV || value > alpha)
788 // Aspiration window is disabled in multi-pv case
790 alpha = -VALUE_INFINITE;
792 // Full depth PV search, done on first move or after a fail high
793 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
797 // Step 14. Reduced search
798 // if the move fails high will be re-searched at full depth
799 bool doFullDepthSearch = true;
801 if ( depth >= 3 * OnePly
803 && !captureOrPromotion
804 && !move_is_castle(move))
806 ss->reduction = reduction<PV>(depth, i - MultiPV + 2);
809 assert(newDepth-ss->reduction >= OnePly);
811 // Reduced depth non-pv search using alpha as upperbound
812 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
813 doFullDepthSearch = (value > alpha);
816 // The move failed high, but if reduction is very big we could
817 // face a false positive, retry with a less aggressive reduction,
818 // if the move fails high again then go with full depth search.
819 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
821 assert(newDepth - OnePly >= OnePly);
823 ss->reduction = OnePly;
824 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, 1);
825 doFullDepthSearch = (value > alpha);
827 ss->reduction = Depth(0); // Restore original reduction
830 // Step 15. Full depth search
831 if (doFullDepthSearch)
833 // Full depth non-pv search using alpha as upperbound
834 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 1);
836 // If we are above alpha then research at same depth but as PV
837 // to get a correct score or eventually a fail high above beta.
839 value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 1);
843 // Step 16. Undo move
846 // Can we exit fail high loop ?
847 if (AbortSearch || value < beta)
850 // We are failing high and going to do a research. It's important to update
851 // the score before research in case we run out of time while researching.
852 rml.set_move_score(i, value);
854 extract_pv_from_tt(pos, move, pv);
855 rml.set_move_pv(i, pv);
857 // Print information to the standard output
858 print_pv_info(pos, pv, alpha, beta, value);
860 // Prepare for a research after a fail high, each time with a wider window
861 *betaPtr = beta = Min(beta + AspirationDelta * (1 << researchCountFH), VALUE_INFINITE);
864 } // End of fail high loop
866 // Finished searching the move. If AbortSearch is true, the search
867 // was aborted because the user interrupted the search or because we
868 // ran out of time. In this case, the return value of the search cannot
869 // be trusted, and we break out of the loop without updating the best
874 // Remember beta-cutoff and searched nodes counts for this move. The
875 // info is used to sort the root moves for the next iteration.
877 ThreadsMgr.get_beta_counters(pos.side_to_move(), our, their);
878 rml.set_beta_counters(i, our, their);
879 rml.set_move_nodes(i, ThreadsMgr.nodes_searched() - nodes);
881 assert(value >= -VALUE_INFINITE && value <= VALUE_INFINITE);
882 assert(value < beta);
884 // Step 17. Check for new best move
885 if (value <= alpha && i >= MultiPV)
886 rml.set_move_score(i, -VALUE_INFINITE);
889 // PV move or new best move!
892 rml.set_move_score(i, value);
894 extract_pv_from_tt(pos, move, pv);
895 rml.set_move_pv(i, pv);
899 // We record how often the best move has been changed in each
900 // iteration. This information is used for time managment: When
901 // the best move changes frequently, we allocate some more time.
903 BestMoveChangesByIteration[Iteration]++;
905 // Print information to the standard output
906 print_pv_info(pos, pv, alpha, beta, value);
908 // Raise alpha to setup proper non-pv search upper bound
915 for (int j = 0; j < Min(MultiPV, rml.move_count()); j++)
917 cout << "info multipv " << j + 1
918 << " score " << value_to_uci(rml.get_move_score(j))
919 << " depth " << (j <= i ? Iteration : Iteration - 1)
920 << " time " << current_search_time()
921 << " nodes " << ThreadsMgr.nodes_searched()
925 for (int k = 0; rml.get_move_pv(j, k) != MOVE_NONE && k < PLY_MAX; k++)
926 cout << rml.get_move_pv(j, k) << " ";
930 alpha = rml.get_move_score(Min(i, MultiPV - 1));
932 } // PV move or new best move
934 assert(alpha >= *alphaPtr);
936 AspirationFailLow = (alpha == *alphaPtr);
938 if (AspirationFailLow && StopOnPonderhit)
939 StopOnPonderhit = false;
942 // Can we exit fail low loop ?
943 if (AbortSearch || !AspirationFailLow)
946 // Prepare for a research after a fail low, each time with a wider window
947 *alphaPtr = alpha = Max(alpha - AspirationDelta * (1 << researchCountFL), -VALUE_INFINITE);
952 // Sort the moves before to return
959 // search<>() is the main search function for both PV and non-PV nodes
961 template <NodeType PvNode>
962 Value search(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
964 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
965 assert(beta > alpha && beta <= VALUE_INFINITE);
966 assert(PvNode || alpha == beta - 1);
967 assert(ply > 0 && ply < PLY_MAX);
968 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
970 Move movesSearched[256];
973 const TTEntry *tte, *ttx;
975 Move ttMove, move, excludedMove, threatMove;
977 Value bestValue, value, oldAlpha;
978 Value refinedValue, nullValue, futilityValueScaled; // Non-PV specific
979 bool isCheck, singleEvasion, singularExtensionNode, moveIsCheck, captureOrPromotion, dangerous;
980 bool mateThreat = false;
982 int threadID = pos.thread();
983 refinedValue = bestValue = value = -VALUE_INFINITE;
986 // Step 1. Initialize node and poll. Polling can abort search
987 ThreadsMgr.incrementNodeCounter(threadID);
988 ss->currentMove = ss->bestMove = threatMove = MOVE_NONE;
989 (ss+2)->killers[0] = (ss+2)->killers[1] = (ss+2)->mateKiller = MOVE_NONE;
991 if (threadID == 0 && ++NodesSincePoll > NodesBetweenPolls)
997 // Step 2. Check for aborted search and immediate draw
998 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1001 if (pos.is_draw() || ply >= PLY_MAX - 1)
1004 // Step 3. Mate distance pruning
1005 alpha = Max(value_mated_in(ply), alpha);
1006 beta = Min(value_mate_in(ply+1), beta);
1010 // Step 4. Transposition table lookup
1012 // We don't want the score of a partial search to overwrite a previous full search
1013 // TT value, so we use a different position key in case of an excluded move exists.
1014 excludedMove = ss->excludedMove;
1015 posKey = excludedMove ? pos.get_exclusion_key() : pos.get_key();
1017 tte = TT.retrieve(posKey);
1018 ttMove = (tte ? tte->move() : MOVE_NONE);
1020 // At PV nodes, we don't use the TT for pruning, but only for move ordering.
1021 // This is to avoid problems in the following areas:
1023 // * Repetition draw detection
1024 // * Fifty move rule detection
1025 // * Searching for a mate
1026 // * Printing of full PV line
1028 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1030 // Refresh tte entry to avoid aging
1031 TT.store(posKey, tte->value(), tte->type(), tte->depth(), ttMove, tte->static_value(), tte->king_danger());
1033 ss->bestMove = ttMove; // Can be MOVE_NONE
1034 return value_from_tt(tte->value(), ply);
1037 // Step 5. Evaluate the position statically and
1038 // update gain statistics of parent move.
1039 isCheck = pos.is_check();
1041 ss->eval = VALUE_NONE;
1044 assert(tte->static_value() != VALUE_NONE);
1046 ss->eval = tte->static_value();
1047 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1048 refinedValue = refine_eval(tte, ss->eval, ply);
1052 refinedValue = ss->eval = evaluate(pos, ei);
1053 TT.store(posKey, VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1056 // Save gain for the parent non-capture move
1057 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1059 // Step 6. Razoring (is omitted in PV nodes)
1061 && depth < RazorDepth
1063 && refinedValue < beta - razor_margin(depth)
1064 && ttMove == MOVE_NONE
1065 && (ss-1)->currentMove != MOVE_NULL
1066 && !value_is_mate(beta)
1067 && !pos.has_pawn_on_7th(pos.side_to_move()))
1069 Value rbeta = beta - razor_margin(depth);
1070 Value v = qsearch<NonPV>(pos, ss, rbeta-1, rbeta, Depth(0), ply);
1072 // Logically we should return (v + razor_margin(depth)), but
1073 // surprisingly this did slightly weaker in tests.
1077 // Step 7. Static null move pruning (is omitted in PV nodes)
1078 // We're betting that the opponent doesn't have a move that will reduce
1079 // the score by more than futility_margin(depth) if we do a null move.
1081 && !ss->skipNullMove
1082 && depth < RazorDepth
1084 && refinedValue >= beta + futility_margin(depth, 0)
1085 && !value_is_mate(beta)
1086 && pos.non_pawn_material(pos.side_to_move()))
1087 return refinedValue - futility_margin(depth, 0);
1089 // Step 8. Null move search with verification search (is omitted in PV nodes)
1090 // When we jump directly to qsearch() we do a null move only if static value is
1091 // at least beta. Otherwise we do a null move if static value is not more than
1092 // NullMoveMargin under beta.
1094 && !ss->skipNullMove
1097 && refinedValue >= beta - (depth >= 4 * OnePly ? NullMoveMargin : 0)
1098 && !value_is_mate(beta)
1099 && pos.non_pawn_material(pos.side_to_move()))
1101 ss->currentMove = MOVE_NULL;
1103 // Null move dynamic reduction based on depth
1104 int R = 3 + (depth >= 5 * OnePly ? depth / 8 : 0);
1106 // Null move dynamic reduction based on value
1107 if (refinedValue - beta > PawnValueMidgame)
1110 pos.do_null_move(st);
1111 (ss+1)->skipNullMove = true;
1113 nullValue = depth-R*OnePly < OnePly ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1114 : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*OnePly, ply+1);
1115 (ss+1)->skipNullMove = false;
1116 pos.undo_null_move();
1118 if (nullValue >= beta)
1120 // Do not return unproven mate scores
1121 if (nullValue >= value_mate_in(PLY_MAX))
1124 if (depth < 6 * OnePly)
1127 // Do verification search at high depths
1128 ss->skipNullMove = true;
1129 Value v = search<NonPV>(pos, ss, alpha, beta, depth-R*OnePly, ply);
1130 ss->skipNullMove = false;
1137 // The null move failed low, which means that we may be faced with
1138 // some kind of threat. If the previous move was reduced, check if
1139 // the move that refuted the null move was somehow connected to the
1140 // move which was reduced. If a connection is found, return a fail
1141 // low score (which will cause the reduced move to fail high in the
1142 // parent node, which will trigger a re-search with full depth).
1143 if (nullValue == value_mated_in(ply + 2))
1146 threatMove = (ss+1)->bestMove;
1147 if ( depth < ThreatDepth
1148 && (ss-1)->reduction
1149 && connected_moves(pos, (ss-1)->currentMove, threatMove))
1154 // Step 9. Internal iterative deepening
1155 if ( depth >= IIDDepth[PvNode]
1156 && ttMove == MOVE_NONE
1157 && (PvNode || (!isCheck && ss->eval >= beta - IIDMargin)))
1159 Depth d = (PvNode ? depth - 2 * OnePly : depth / 2);
1161 ss->skipNullMove = true;
1162 search<PvNode>(pos, ss, alpha, beta, d, ply);
1163 ss->skipNullMove = false;
1165 ttMove = ss->bestMove;
1166 tte = TT.retrieve(posKey);
1169 // Expensive mate threat detection (only for PV nodes)
1171 mateThreat = pos.has_mate_threat(opposite_color(pos.side_to_move()));
1173 // Initialize a MovePicker object for the current position
1174 MovePicker mp = MovePicker(pos, ttMove, depth, H, ss, (PvNode ? -VALUE_INFINITE : beta));
1176 ss->bestMove = MOVE_NONE;
1177 singleEvasion = isCheck && mp.number_of_evasions() == 1;
1178 singularExtensionNode = depth >= SingularExtensionDepth[PvNode]
1181 && !excludedMove // Do not allow recursive singular extension search
1182 && is_lower_bound(tte->type())
1183 && tte->depth() >= depth - 3 * OnePly;
1185 // Step 10. Loop through moves
1186 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1187 while ( bestValue < beta
1188 && (move = mp.get_next_move()) != MOVE_NONE
1189 && !ThreadsMgr.thread_should_stop(threadID))
1191 assert(move_is_ok(move));
1193 if (move == excludedMove)
1196 moveIsCheck = pos.move_is_check(move, ci);
1197 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1199 // Step 11. Decide the new search depth
1200 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, singleEvasion, mateThreat, &dangerous);
1202 // Singular extension search. If all moves but one fail low on a search of (alpha-s, beta-s),
1203 // and just one fails high on (alpha, beta), then that move is singular and should be extended.
1204 // To verify this we do a reduced search on all the other moves but the ttMove, if result is
1205 // lower then ttValue minus a margin then we extend ttMove.
1206 if ( singularExtensionNode
1207 && move == tte->move()
1210 // Avoid to do an expensive singular extension search on nodes where
1211 // such search have already been done in the past, so assume the last
1212 // singular extension search result is still valid.
1214 && depth < SingularExtensionDepth[PvNode] + 5 * OnePly
1215 && (ttx = TT.retrieve(pos.get_exclusion_key())) != NULL)
1217 if (is_upper_bound(ttx->type()))
1220 singularExtensionNode = false;
1223 Value ttValue = value_from_tt(tte->value(), ply);
1225 if (singularExtensionNode && abs(ttValue) < VALUE_KNOWN_WIN)
1227 Value b = ttValue - SingularExtensionMargin;
1228 ss->excludedMove = move;
1229 ss->skipNullMove = true;
1230 Value v = search<NonPV>(pos, ss, b - 1, b, depth / 2, ply);
1231 ss->skipNullMove = false;
1232 ss->excludedMove = MOVE_NONE;
1233 ss->bestMove = MOVE_NONE;
1239 newDepth = depth - OnePly + ext;
1241 // Update current move (this must be done after singular extension search)
1242 movesSearched[moveCount++] = ss->currentMove = move;
1244 // Step 12. Futility pruning (is omitted in PV nodes)
1246 && !captureOrPromotion
1250 && !move_is_castle(move))
1252 // Move count based pruning
1253 if ( moveCount >= futility_move_count(depth)
1254 && !(threatMove && connected_threat(pos, move, threatMove))
1255 && bestValue > value_mated_in(PLY_MAX))
1258 // Value based pruning
1259 // We illogically ignore reduction condition depth >= 3*OnePly for predicted depth,
1260 // but fixing this made program slightly weaker.
1261 Depth predictedDepth = newDepth - reduction<NonPV>(depth, moveCount);
1262 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1263 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1265 if (futilityValueScaled < beta)
1267 if (futilityValueScaled > bestValue)
1268 bestValue = futilityValueScaled;
1273 // Step 13. Make the move
1274 pos.do_move(move, st, ci, moveIsCheck);
1276 // Step extra. pv search (only in PV nodes)
1277 // The first move in list is the expected PV
1278 if (PvNode && moveCount == 1)
1279 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1280 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1283 // Step 14. Reduced depth search
1284 // If the move fails high will be re-searched at full depth.
1285 bool doFullDepthSearch = true;
1287 if ( depth >= 3 * OnePly
1288 && !captureOrPromotion
1290 && !move_is_castle(move)
1291 && !move_is_killer(move, ss))
1293 ss->reduction = reduction<PvNode>(depth, moveCount);
1296 Depth d = newDepth - ss->reduction;
1297 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1298 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, ply+1);
1300 doFullDepthSearch = (value > alpha);
1303 // The move failed high, but if reduction is very big we could
1304 // face a false positive, retry with a less aggressive reduction,
1305 // if the move fails high again then go with full depth search.
1306 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1308 assert(newDepth - OnePly >= OnePly);
1310 ss->reduction = OnePly;
1311 value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth-ss->reduction, ply+1);
1312 doFullDepthSearch = (value > alpha);
1314 ss->reduction = Depth(0); // Restore original reduction
1317 // Step 15. Full depth search
1318 if (doFullDepthSearch)
1320 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(alpha+1), -alpha, Depth(0), ply+1)
1321 : - search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, ply+1);
1323 // Step extra. pv search (only in PV nodes)
1324 // Search only for possible new PV nodes, if instead value >= beta then
1325 // parent node fails low with value <= alpha and tries another move.
1326 if (PvNode && value > alpha && value < beta)
1327 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -beta, -alpha, Depth(0), ply+1)
1328 : - search<PV>(pos, ss+1, -beta, -alpha, newDepth, ply+1);
1332 // Step 16. Undo move
1333 pos.undo_move(move);
1335 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1337 // Step 17. Check for new best move
1338 if (value > bestValue)
1343 if (PvNode && value < beta) // We want always alpha < beta
1346 if (value == value_mate_in(ply + 1))
1347 ss->mateKiller = move;
1349 ss->bestMove = move;
1353 // Step 18. Check for split
1354 if ( depth >= MinimumSplitDepth
1355 && ThreadsMgr.active_threads() > 1
1357 && ThreadsMgr.available_thread_exists(threadID)
1359 && !ThreadsMgr.thread_should_stop(threadID)
1361 ThreadsMgr.split<FakeSplit>(pos, ss, ply, &alpha, beta, &bestValue, depth,
1362 threatMove, mateThreat, &moveCount, &mp, PvNode);
1365 // Step 19. Check for mate and stalemate
1366 // All legal moves have been searched and if there are
1367 // no legal moves, it must be mate or stalemate.
1368 // If one move was excluded return fail low score.
1370 return excludedMove ? oldAlpha : isCheck ? value_mated_in(ply) : VALUE_DRAW;
1372 // Step 20. Update tables
1373 // If the search is not aborted, update the transposition table,
1374 // history counters, and killer moves.
1375 if (AbortSearch || ThreadsMgr.thread_should_stop(threadID))
1378 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1379 move = (bestValue <= oldAlpha ? MOVE_NONE : ss->bestMove);
1380 TT.store(posKey, value_to_tt(bestValue, ply), vt, depth, move, ss->eval, ei.kingDanger[pos.side_to_move()]);
1382 // Update killers and history only for non capture moves that fails high
1383 if (bestValue >= beta)
1385 ThreadsMgr.incrementBetaCounter(pos.side_to_move(), depth, threadID);
1386 if (!pos.move_is_capture_or_promotion(move))
1388 update_history(pos, move, depth, movesSearched, moveCount);
1389 update_killers(move, ss);
1393 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1399 // qsearch() is the quiescence search function, which is called by the main
1400 // search function when the remaining depth is zero (or, to be more precise,
1401 // less than OnePly).
1403 template <NodeType PvNode>
1404 Value qsearch(Position& pos, SearchStack* ss, Value alpha, Value beta, Depth depth, int ply) {
1406 assert(alpha >= -VALUE_INFINITE && alpha <= VALUE_INFINITE);
1407 assert(beta >= -VALUE_INFINITE && beta <= VALUE_INFINITE);
1408 assert(PvNode || alpha == beta - 1);
1410 assert(ply > 0 && ply < PLY_MAX);
1411 assert(pos.thread() >= 0 && pos.thread() < ThreadsMgr.active_threads());
1416 Value bestValue, value, futilityValue, futilityBase;
1417 bool isCheck, deepChecks, enoughMaterial, moveIsCheck, evasionPrunable;
1419 Value oldAlpha = alpha;
1421 ThreadsMgr.incrementNodeCounter(pos.thread());
1422 ss->bestMove = ss->currentMove = MOVE_NONE;
1424 // Check for an instant draw or maximum ply reached
1425 if (pos.is_draw() || ply >= PLY_MAX - 1)
1428 // Transposition table lookup. At PV nodes, we don't use the TT for
1429 // pruning, but only for move ordering.
1430 tte = TT.retrieve(pos.get_key());
1431 ttMove = (tte ? tte->move() : MOVE_NONE);
1433 if (!PvNode && tte && ok_to_use_TT(tte, depth, beta, ply))
1435 ss->bestMove = ttMove; // Can be MOVE_NONE
1436 return value_from_tt(tte->value(), ply);
1439 isCheck = pos.is_check();
1441 // Evaluate the position statically
1444 bestValue = futilityBase = -VALUE_INFINITE;
1445 ss->eval = VALUE_NONE;
1446 deepChecks = enoughMaterial = false;
1452 assert(tte->static_value() != VALUE_NONE);
1454 ei.kingDanger[pos.side_to_move()] = tte->king_danger();
1455 bestValue = tte->static_value();
1458 bestValue = evaluate(pos, ei);
1460 ss->eval = bestValue;
1461 update_gains(pos, (ss-1)->currentMove, (ss-1)->eval, ss->eval);
1463 // Stand pat. Return immediately if static value is at least beta
1464 if (bestValue >= beta)
1467 TT.store(pos.get_key(), value_to_tt(bestValue, ply), VALUE_TYPE_LOWER, DEPTH_NONE, MOVE_NONE, ss->eval, ei.kingDanger[pos.side_to_move()]);
1472 if (PvNode && bestValue > alpha)
1475 // If we are near beta then try to get a cutoff pushing checks a bit further
1476 deepChecks = (depth == -OnePly && bestValue >= beta - PawnValueMidgame / 8);
1478 // Futility pruning parameters, not needed when in check
1479 futilityBase = bestValue + FutilityMarginQS + ei.kingDanger[pos.side_to_move()];
1480 enoughMaterial = pos.non_pawn_material(pos.side_to_move()) > RookValueMidgame;
1483 // Initialize a MovePicker object for the current position, and prepare
1484 // to search the moves. Because the depth is <= 0 here, only captures,
1485 // queen promotions and checks (only if depth == 0 or depth == -OnePly
1486 // and we are near beta) will be generated.
1487 MovePicker mp = MovePicker(pos, ttMove, deepChecks ? Depth(0) : depth, H);
1490 // Loop through the moves until no moves remain or a beta cutoff occurs
1491 while ( alpha < beta
1492 && (move = mp.get_next_move()) != MOVE_NONE)
1494 assert(move_is_ok(move));
1496 moveIsCheck = pos.move_is_check(move, ci);
1504 && !move_is_promotion(move)
1505 && !pos.move_is_passed_pawn_push(move))
1507 futilityValue = futilityBase
1508 + pos.endgame_value_of_piece_on(move_to(move))
1509 + (move_is_ep(move) ? PawnValueEndgame : Value(0));
1511 if (futilityValue < alpha)
1513 if (futilityValue > bestValue)
1514 bestValue = futilityValue;
1519 // Detect blocking evasions that are candidate to be pruned
1520 evasionPrunable = isCheck
1521 && bestValue > value_mated_in(PLY_MAX)
1522 && !pos.move_is_capture(move)
1523 && pos.type_of_piece_on(move_from(move)) != KING
1524 && !pos.can_castle(pos.side_to_move());
1526 // Don't search moves with negative SEE values
1528 && (!isCheck || evasionPrunable)
1530 && !move_is_promotion(move)
1531 && pos.see_sign(move) < 0)
1534 // Update current move
1535 ss->currentMove = move;
1537 // Make and search the move
1538 pos.do_move(move, st, ci, moveIsCheck);
1539 value = -qsearch<PvNode>(pos, ss+1, -beta, -alpha, depth-OnePly, ply+1);
1540 pos.undo_move(move);
1542 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1545 if (value > bestValue)
1551 ss->bestMove = move;
1556 // All legal moves have been searched. A special case: If we're in check
1557 // and no legal moves were found, it is checkmate.
1558 if (isCheck && bestValue == -VALUE_INFINITE)
1559 return value_mated_in(ply);
1561 // Update transposition table
1562 Depth d = (depth == Depth(0) ? Depth(0) : Depth(-1));
1563 ValueType vt = (bestValue <= oldAlpha ? VALUE_TYPE_UPPER : bestValue >= beta ? VALUE_TYPE_LOWER : VALUE_TYPE_EXACT);
1564 TT.store(pos.get_key(), value_to_tt(bestValue, ply), vt, d, ss->bestMove, ss->eval, ei.kingDanger[pos.side_to_move()]);
1566 // Update killers only for checking moves that fails high
1567 if ( bestValue >= beta
1568 && !pos.move_is_capture_or_promotion(ss->bestMove))
1569 update_killers(ss->bestMove, ss);
1571 assert(bestValue > -VALUE_INFINITE && bestValue < VALUE_INFINITE);
1577 // sp_search() is used to search from a split point. This function is called
1578 // by each thread working at the split point. It is similar to the normal
1579 // search() function, but simpler. Because we have already probed the hash
1580 // table, done a null move search, and searched the first move before
1581 // splitting, we don't have to repeat all this work in sp_search(). We
1582 // also don't need to store anything to the hash table here: This is taken
1583 // care of after we return from the split point.
1585 template <NodeType PvNode>
1586 void sp_search(SplitPoint* sp, int threadID) {
1588 assert(threadID >= 0 && threadID < ThreadsMgr.active_threads());
1589 assert(ThreadsMgr.active_threads() > 1);
1593 Depth ext, newDepth;
1595 Value futilityValueScaled; // NonPV specific
1596 bool isCheck, moveIsCheck, captureOrPromotion, dangerous;
1598 value = -VALUE_INFINITE;
1600 Position pos(*sp->pos, threadID);
1602 SearchStack* ss = sp->sstack[threadID] + 1;
1603 isCheck = pos.is_check();
1605 // Step 10. Loop through moves
1606 // Loop through all legal moves until no moves remain or a beta cutoff occurs
1607 lock_grab(&(sp->lock));
1609 while ( sp->bestValue < sp->beta
1610 && (move = sp->mp->get_next_move()) != MOVE_NONE
1611 && !ThreadsMgr.thread_should_stop(threadID))
1613 moveCount = ++sp->moveCount;
1614 lock_release(&(sp->lock));
1616 assert(move_is_ok(move));
1618 moveIsCheck = pos.move_is_check(move, ci);
1619 captureOrPromotion = pos.move_is_capture_or_promotion(move);
1621 // Step 11. Decide the new search depth
1622 ext = extension<PvNode>(pos, move, captureOrPromotion, moveIsCheck, false, sp->mateThreat, &dangerous);
1623 newDepth = sp->depth - OnePly + ext;
1625 // Update current move
1626 ss->currentMove = move;
1628 // Step 12. Futility pruning (is omitted in PV nodes)
1630 && !captureOrPromotion
1633 && !move_is_castle(move))
1635 // Move count based pruning
1636 if ( moveCount >= futility_move_count(sp->depth)
1637 && !(sp->threatMove && connected_threat(pos, move, sp->threatMove))
1638 && sp->bestValue > value_mated_in(PLY_MAX))
1640 lock_grab(&(sp->lock));
1644 // Value based pruning
1645 Depth predictedDepth = newDepth - reduction<NonPV>(sp->depth, moveCount);
1646 futilityValueScaled = ss->eval + futility_margin(predictedDepth, moveCount)
1647 + H.gain(pos.piece_on(move_from(move)), move_to(move));
1649 if (futilityValueScaled < sp->beta)
1651 lock_grab(&(sp->lock));
1653 if (futilityValueScaled > sp->bestValue)
1654 sp->bestValue = futilityValueScaled;
1659 // Step 13. Make the move
1660 pos.do_move(move, st, ci, moveIsCheck);
1662 // Step 14. Reduced search
1663 // If the move fails high will be re-searched at full depth.
1664 bool doFullDepthSearch = true;
1666 if ( !captureOrPromotion
1668 && !move_is_castle(move)
1669 && !move_is_killer(move, ss))
1671 ss->reduction = reduction<PvNode>(sp->depth, moveCount);
1674 Value localAlpha = sp->alpha;
1675 Depth d = newDepth - ss->reduction;
1676 value = d < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1677 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, d, sp->ply+1);
1679 doFullDepthSearch = (value > localAlpha);
1682 // The move failed high, but if reduction is very big we could
1683 // face a false positive, retry with a less aggressive reduction,
1684 // if the move fails high again then go with full depth search.
1685 if (doFullDepthSearch && ss->reduction > 2 * OnePly)
1687 assert(newDepth - OnePly >= OnePly);
1689 ss->reduction = OnePly;
1690 Value localAlpha = sp->alpha;
1691 value = -search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth-ss->reduction, sp->ply+1);
1692 doFullDepthSearch = (value > localAlpha);
1694 ss->reduction = Depth(0); // Restore original reduction
1697 // Step 15. Full depth search
1698 if (doFullDepthSearch)
1700 Value localAlpha = sp->alpha;
1701 value = newDepth < OnePly ? -qsearch<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, Depth(0), sp->ply+1)
1702 : - search<NonPV>(pos, ss+1, -(localAlpha+1), -localAlpha, newDepth, sp->ply+1);
1704 // Step extra. pv search (only in PV nodes)
1705 // Search only for possible new PV nodes, if instead value >= beta then
1706 // parent node fails low with value <= alpha and tries another move.
1707 if (PvNode && value > localAlpha && value < sp->beta)
1708 value = newDepth < OnePly ? -qsearch<PV>(pos, ss+1, -sp->beta, -sp->alpha, Depth(0), sp->ply+1)
1709 : - search<PV>(pos, ss+1, -sp->beta, -sp->alpha, newDepth, sp->ply+1);
1712 // Step 16. Undo move
1713 pos.undo_move(move);
1715 assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
1717 // Step 17. Check for new best move
1718 lock_grab(&(sp->lock));
1720 if (value > sp->bestValue && !ThreadsMgr.thread_should_stop(threadID))
1722 sp->bestValue = value;
1724 if (sp->bestValue > sp->alpha)
1726 if (!PvNode || value >= sp->beta)
1727 sp->stopRequest = true;
1729 if (PvNode && value < sp->beta) // This guarantees that always: sp->alpha < sp->beta
1732 sp->parentSstack->bestMove = ss->bestMove = move;
1737 /* Here we have the lock still grabbed */
1739 sp->slaves[threadID] = 0;
1741 lock_release(&(sp->lock));
1745 // connected_moves() tests whether two moves are 'connected' in the sense
1746 // that the first move somehow made the second move possible (for instance
1747 // if the moving piece is the same in both moves). The first move is assumed
1748 // to be the move that was made to reach the current position, while the
1749 // second move is assumed to be a move from the current position.
1751 bool connected_moves(const Position& pos, Move m1, Move m2) {
1753 Square f1, t1, f2, t2;
1756 assert(move_is_ok(m1));
1757 assert(move_is_ok(m2));
1759 if (m2 == MOVE_NONE)
1762 // Case 1: The moving piece is the same in both moves
1768 // Case 2: The destination square for m2 was vacated by m1
1774 // Case 3: Moving through the vacated square
1775 if ( piece_is_slider(pos.piece_on(f2))
1776 && bit_is_set(squares_between(f2, t2), f1))
1779 // Case 4: The destination square for m2 is defended by the moving piece in m1
1780 p = pos.piece_on(t1);
1781 if (bit_is_set(pos.attacks_from(p, t1), t2))
1784 // Case 5: Discovered check, checking piece is the piece moved in m1
1785 if ( piece_is_slider(p)
1786 && bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), f2)
1787 && !bit_is_set(squares_between(t1, pos.king_square(pos.side_to_move())), t2))
1789 // discovered_check_candidates() works also if the Position's side to
1790 // move is the opposite of the checking piece.
1791 Color them = opposite_color(pos.side_to_move());
1792 Bitboard dcCandidates = pos.discovered_check_candidates(them);
1794 if (bit_is_set(dcCandidates, f2))
1801 // value_is_mate() checks if the given value is a mate one eventually
1802 // compensated for the ply.
1804 bool value_is_mate(Value value) {
1806 assert(abs(value) <= VALUE_INFINITE);
1808 return value <= value_mated_in(PLY_MAX)
1809 || value >= value_mate_in(PLY_MAX);
1813 // value_to_tt() adjusts a mate score from "plies to mate from the root" to
1814 // "plies to mate from the current ply". Non-mate scores are unchanged.
1815 // The function is called before storing a value to the transposition table.
1817 Value value_to_tt(Value v, int ply) {
1819 if (v >= value_mate_in(PLY_MAX))
1822 if (v <= value_mated_in(PLY_MAX))
1829 // value_from_tt() is the inverse of value_to_tt(): It adjusts a mate score from
1830 // the transposition table to a mate score corrected for the current ply.
1832 Value value_from_tt(Value v, int ply) {
1834 if (v >= value_mate_in(PLY_MAX))
1837 if (v <= value_mated_in(PLY_MAX))
1844 // move_is_killer() checks if the given move is among the killer moves
1846 bool move_is_killer(Move m, SearchStack* ss) {
1848 if (ss->killers[0] == m || ss->killers[1] == m)
1855 // extension() decides whether a move should be searched with normal depth,
1856 // or with extended depth. Certain classes of moves (checking moves, in
1857 // particular) are searched with bigger depth than ordinary moves and in
1858 // any case are marked as 'dangerous'. Note that also if a move is not
1859 // extended, as example because the corresponding UCI option is set to zero,
1860 // the move is marked as 'dangerous' so, at least, we avoid to prune it.
1861 template <NodeType PvNode>
1862 Depth extension(const Position& pos, Move m, bool captureOrPromotion, bool moveIsCheck,
1863 bool singleEvasion, bool mateThreat, bool* dangerous) {
1865 assert(m != MOVE_NONE);
1867 Depth result = Depth(0);
1868 *dangerous = moveIsCheck | singleEvasion | mateThreat;
1872 if (moveIsCheck && pos.see_sign(m) >= 0)
1873 result += CheckExtension[PvNode];
1876 result += SingleEvasionExtension[PvNode];
1879 result += MateThreatExtension[PvNode];
1882 if (pos.type_of_piece_on(move_from(m)) == PAWN)
1884 Color c = pos.side_to_move();
1885 if (relative_rank(c, move_to(m)) == RANK_7)
1887 result += PawnPushTo7thExtension[PvNode];
1890 if (pos.pawn_is_passed(c, move_to(m)))
1892 result += PassedPawnExtension[PvNode];
1897 if ( captureOrPromotion
1898 && pos.type_of_piece_on(move_to(m)) != PAWN
1899 && ( pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK)
1900 - pos.midgame_value_of_piece_on(move_to(m)) == Value(0))
1901 && !move_is_promotion(m)
1904 result += PawnEndgameExtension[PvNode];
1909 && captureOrPromotion
1910 && pos.type_of_piece_on(move_to(m)) != PAWN
1911 && pos.see_sign(m) >= 0)
1917 return Min(result, OnePly);
1921 // connected_threat() tests whether it is safe to forward prune a move or if
1922 // is somehow coonected to the threat move returned by null search.
1924 bool connected_threat(const Position& pos, Move m, Move threat) {
1926 assert(move_is_ok(m));
1927 assert(threat && move_is_ok(threat));
1928 assert(!pos.move_is_check(m));
1929 assert(!pos.move_is_capture_or_promotion(m));
1930 assert(!pos.move_is_passed_pawn_push(m));
1932 Square mfrom, mto, tfrom, tto;
1934 mfrom = move_from(m);
1936 tfrom = move_from(threat);
1937 tto = move_to(threat);
1939 // Case 1: Don't prune moves which move the threatened piece
1943 // Case 2: If the threatened piece has value less than or equal to the
1944 // value of the threatening piece, don't prune move which defend it.
1945 if ( pos.move_is_capture(threat)
1946 && ( pos.midgame_value_of_piece_on(tfrom) >= pos.midgame_value_of_piece_on(tto)
1947 || pos.type_of_piece_on(tfrom) == KING)
1948 && pos.move_attacks_square(m, tto))
1951 // Case 3: If the moving piece in the threatened move is a slider, don't
1952 // prune safe moves which block its ray.
1953 if ( piece_is_slider(pos.piece_on(tfrom))
1954 && bit_is_set(squares_between(tfrom, tto), mto)
1955 && pos.see_sign(m) >= 0)
1962 // ok_to_use_TT() returns true if a transposition table score
1963 // can be used at a given point in search.
1965 bool ok_to_use_TT(const TTEntry* tte, Depth depth, Value beta, int ply) {
1967 Value v = value_from_tt(tte->value(), ply);
1969 return ( tte->depth() >= depth
1970 || v >= Max(value_mate_in(PLY_MAX), beta)
1971 || v < Min(value_mated_in(PLY_MAX), beta))
1973 && ( (is_lower_bound(tte->type()) && v >= beta)
1974 || (is_upper_bound(tte->type()) && v < beta));
1978 // refine_eval() returns the transposition table score if
1979 // possible otherwise falls back on static position evaluation.
1981 Value refine_eval(const TTEntry* tte, Value defaultEval, int ply) {
1985 Value v = value_from_tt(tte->value(), ply);
1987 if ( (is_lower_bound(tte->type()) && v >= defaultEval)
1988 || (is_upper_bound(tte->type()) && v < defaultEval))
1995 // update_history() registers a good move that produced a beta-cutoff
1996 // in history and marks as failures all the other moves of that ply.
1998 void update_history(const Position& pos, Move move, Depth depth,
1999 Move movesSearched[], int moveCount) {
2003 H.success(pos.piece_on(move_from(move)), move_to(move), depth);
2005 for (int i = 0; i < moveCount - 1; i++)
2007 m = movesSearched[i];
2011 if (!pos.move_is_capture_or_promotion(m))
2012 H.failure(pos.piece_on(move_from(m)), move_to(m), depth);
2017 // update_killers() add a good move that produced a beta-cutoff
2018 // among the killer moves of that ply.
2020 void update_killers(Move m, SearchStack* ss) {
2022 if (m == ss->killers[0])
2025 ss->killers[1] = ss->killers[0];
2030 // update_gains() updates the gains table of a non-capture move given
2031 // the static position evaluation before and after the move.
2033 void update_gains(const Position& pos, Move m, Value before, Value after) {
2036 && before != VALUE_NONE
2037 && after != VALUE_NONE
2038 && pos.captured_piece() == NO_PIECE_TYPE
2039 && !move_is_special(m))
2040 H.set_gain(pos.piece_on(move_to(m)), move_to(m), -(before + after));
2044 // current_search_time() returns the number of milliseconds which have passed
2045 // since the beginning of the current search.
2047 int current_search_time() {
2049 return get_system_time() - SearchStartTime;
2053 // value_to_uci() converts a value to a string suitable for use with the UCI protocol
2055 std::string value_to_uci(Value v) {
2057 std::stringstream s;
2059 if (abs(v) < VALUE_MATE - PLY_MAX * OnePly)
2060 s << "cp " << int(v) * 100 / int(PawnValueMidgame); // Scale to pawn = 100
2062 s << "mate " << (v > 0 ? (VALUE_MATE - v + 1) / 2 : -(VALUE_MATE + v) / 2 );
2067 // nps() computes the current nodes/second count.
2071 int t = current_search_time();
2072 return (t > 0 ? int((ThreadsMgr.nodes_searched() * 1000) / t) : 0);
2076 // poll() performs two different functions: It polls for user input, and it
2077 // looks at the time consumed so far and decides if it's time to abort the
2082 static int lastInfoTime;
2083 int t = current_search_time();
2088 // We are line oriented, don't read single chars
2089 std::string command;
2091 if (!std::getline(std::cin, command))
2094 if (command == "quit")
2097 PonderSearch = false;
2101 else if (command == "stop")
2104 PonderSearch = false;
2106 else if (command == "ponderhit")
2110 // Print search information
2114 else if (lastInfoTime > t)
2115 // HACK: Must be a new search where we searched less than
2116 // NodesBetweenPolls nodes during the first second of search.
2119 else if (t - lastInfoTime >= 1000)
2126 if (dbg_show_hit_rate)
2127 dbg_print_hit_rate();
2129 cout << "info nodes " << ThreadsMgr.nodes_searched() << " nps " << nps()
2130 << " time " << t << endl;
2133 // Should we stop the search?
2137 bool stillAtFirstMove = FirstRootMove
2138 && !AspirationFailLow
2139 && t > TimeMgr.available_time();
2141 bool noMoreTime = t > TimeMgr.maximum_time()
2142 || stillAtFirstMove;
2144 if ( (Iteration >= 3 && UseTimeManagement && noMoreTime)
2145 || (ExactMaxTime && t >= ExactMaxTime)
2146 || (Iteration >= 3 && MaxNodes && ThreadsMgr.nodes_searched() >= MaxNodes))
2151 // ponderhit() is called when the program is pondering (i.e. thinking while
2152 // it's the opponent's turn to move) in order to let the engine know that
2153 // it correctly predicted the opponent's move.
2157 int t = current_search_time();
2158 PonderSearch = false;
2160 bool stillAtFirstMove = FirstRootMove
2161 && !AspirationFailLow
2162 && t > TimeMgr.available_time();
2164 bool noMoreTime = t > TimeMgr.maximum_time()
2165 || stillAtFirstMove;
2167 if (Iteration >= 3 && UseTimeManagement && (noMoreTime || StopOnPonderhit))
2172 // init_ss_array() does a fast reset of the first entries of a SearchStack
2173 // array and of all the excludedMove and skipNullMove entries.
2175 void init_ss_array(SearchStack* ss, int size) {
2177 for (int i = 0; i < size; i++, ss++)
2179 ss->excludedMove = MOVE_NONE;
2180 ss->skipNullMove = false;
2181 ss->reduction = Depth(0);
2184 ss->killers[0] = ss->killers[1] = ss->mateKiller = MOVE_NONE;
2189 // wait_for_stop_or_ponderhit() is called when the maximum depth is reached
2190 // while the program is pondering. The point is to work around a wrinkle in
2191 // the UCI protocol: When pondering, the engine is not allowed to give a
2192 // "bestmove" before the GUI sends it a "stop" or "ponderhit" command.
2193 // We simply wait here until one of these commands is sent, and return,
2194 // after which the bestmove and pondermove will be printed (in id_loop()).
2196 void wait_for_stop_or_ponderhit() {
2198 std::string command;
2202 if (!std::getline(std::cin, command))
2205 if (command == "quit")
2210 else if (command == "ponderhit" || command == "stop")
2216 // print_pv_info() prints to standard output and eventually to log file information on
2217 // the current PV line. It is called at each iteration or after a new pv is found.
2219 void print_pv_info(const Position& pos, Move pv[], Value alpha, Value beta, Value value) {
2221 cout << "info depth " << Iteration
2222 << " score " << value_to_uci(value)
2223 << (value >= beta ? " lowerbound" : value <= alpha ? " upperbound" : "")
2224 << " time " << current_search_time()
2225 << " nodes " << ThreadsMgr.nodes_searched()
2229 for (Move* m = pv; *m != MOVE_NONE; m++)
2236 ValueType t = value >= beta ? VALUE_TYPE_LOWER :
2237 value <= alpha ? VALUE_TYPE_UPPER : VALUE_TYPE_EXACT;
2239 LogFile << pretty_pv(pos, current_search_time(), Iteration,
2240 ThreadsMgr.nodes_searched(), value, t, pv) << endl;
2245 // insert_pv_in_tt() is called at the end of a search iteration, and inserts
2246 // the PV back into the TT. This makes sure the old PV moves are searched
2247 // first, even if the old TT entries have been overwritten.
2249 void insert_pv_in_tt(const Position& pos, Move pv[]) {
2253 Position p(pos, pos.thread());
2257 for (int i = 0; pv[i] != MOVE_NONE; i++)
2259 tte = TT.retrieve(p.get_key());
2260 if (!tte || tte->move() != pv[i])
2262 v = (p.is_check() ? VALUE_NONE : evaluate(p, ei));
2263 TT.store(p.get_key(), VALUE_NONE, VALUE_TYPE_NONE, DEPTH_NONE, pv[i], v, ei.kingDanger[pos.side_to_move()]);
2265 p.do_move(pv[i], st);
2270 // extract_pv_from_tt() builds a PV by adding moves from the transposition table.
2271 // We consider also failing high nodes and not only VALUE_TYPE_EXACT nodes. This
2272 // allow to always have a ponder move even when we fail high at root and also a
2273 // long PV to print that is important for position analysis.
2275 void extract_pv_from_tt(const Position& pos, Move bestMove, Move pv[]) {
2279 Position p(pos, pos.thread());
2282 assert(bestMove != MOVE_NONE);
2285 p.do_move(pv[ply++], st);
2287 while ( (tte = TT.retrieve(p.get_key())) != NULL
2288 && tte->move() != MOVE_NONE
2289 && move_is_legal(p, tte->move())
2291 && (!p.is_draw() || ply < 2))
2293 pv[ply] = tte->move();
2294 p.do_move(pv[ply++], st);
2296 pv[ply] = MOVE_NONE;
2300 // init_thread() is the function which is called when a new thread is
2301 // launched. It simply calls the idle_loop() function with the supplied
2302 // threadID. There are two versions of this function; one for POSIX
2303 // threads and one for Windows threads.
2305 #if !defined(_MSC_VER)
2307 void* init_thread(void *threadID) {
2309 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2315 DWORD WINAPI init_thread(LPVOID threadID) {
2317 ThreadsMgr.idle_loop(*(int*)threadID, NULL);
2324 /// The ThreadsManager class
2326 // resetNodeCounters(), resetBetaCounters(), searched_nodes() and
2327 // get_beta_counters() are getters/setters for the per thread
2328 // counters used to sort the moves at root.
2330 void ThreadsManager::resetNodeCounters() {
2332 for (int i = 0; i < MAX_THREADS; i++)
2333 threads[i].nodes = 0ULL;
2336 void ThreadsManager::resetBetaCounters() {
2338 for (int i = 0; i < MAX_THREADS; i++)
2339 threads[i].betaCutOffs[WHITE] = threads[i].betaCutOffs[BLACK] = 0ULL;
2342 int64_t ThreadsManager::nodes_searched() const {
2344 int64_t result = 0ULL;
2345 for (int i = 0; i < ActiveThreads; i++)
2346 result += threads[i].nodes;
2351 void ThreadsManager::get_beta_counters(Color us, int64_t& our, int64_t& their) const {
2354 for (int i = 0; i < MAX_THREADS; i++)
2356 our += threads[i].betaCutOffs[us];
2357 their += threads[i].betaCutOffs[opposite_color(us)];
2362 // idle_loop() is where the threads are parked when they have no work to do.
2363 // The parameter 'sp', if non-NULL, is a pointer to an active SplitPoint
2364 // object for which the current thread is the master.
2366 void ThreadsManager::idle_loop(int threadID, SplitPoint* sp) {
2368 assert(threadID >= 0 && threadID < MAX_THREADS);
2372 // Slave threads can exit as soon as AllThreadsShouldExit raises,
2373 // master should exit as last one.
2374 if (AllThreadsShouldExit)
2377 threads[threadID].state = THREAD_TERMINATED;
2381 // If we are not thinking, wait for a condition to be signaled
2382 // instead of wasting CPU time polling for work.
2383 while (AllThreadsShouldSleep || threadID >= ActiveThreads)
2386 assert(threadID != 0);
2387 threads[threadID].state = THREAD_SLEEPING;
2389 #if !defined(_MSC_VER)
2390 lock_grab(&WaitLock);
2391 if (AllThreadsShouldSleep || threadID >= ActiveThreads)
2392 pthread_cond_wait(&WaitCond, &WaitLock);
2393 lock_release(&WaitLock);
2395 WaitForSingleObject(SitIdleEvent[threadID], INFINITE);
2399 // If thread has just woken up, mark it as available
2400 if (threads[threadID].state == THREAD_SLEEPING)
2401 threads[threadID].state = THREAD_AVAILABLE;
2403 // If this thread has been assigned work, launch a search
2404 if (threads[threadID].state == THREAD_WORKISWAITING)
2406 assert(!AllThreadsShouldExit && !AllThreadsShouldSleep);
2408 threads[threadID].state = THREAD_SEARCHING;
2410 if (threads[threadID].splitPoint->pvNode)
2411 sp_search<PV>(threads[threadID].splitPoint, threadID);
2413 sp_search<NonPV>(threads[threadID].splitPoint, threadID);
2415 assert(threads[threadID].state == THREAD_SEARCHING);
2417 threads[threadID].state = THREAD_AVAILABLE;
2420 // If this thread is the master of a split point and all slaves have
2421 // finished their work at this split point, return from the idle loop.
2423 for ( ; sp && i < ActiveThreads && !sp->slaves[i]; i++) {}
2425 if (i == ActiveThreads)
2427 // Because sp->slaves[] is reset under lock protection,
2428 // be sure sp->lock has been released before to return.
2429 lock_grab(&(sp->lock));
2430 lock_release(&(sp->lock));
2432 assert(threads[threadID].state == THREAD_AVAILABLE);
2434 threads[threadID].state = THREAD_SEARCHING;
2441 // init_threads() is called during startup. It launches all helper threads,
2442 // and initializes the split point stack and the global locks and condition
2445 void ThreadsManager::init_threads() {
2450 #if !defined(_MSC_VER)
2451 pthread_t pthread[1];
2454 // Initialize global locks
2456 lock_init(&WaitLock);
2458 #if !defined(_MSC_VER)
2459 pthread_cond_init(&WaitCond, NULL);
2461 for (i = 0; i < MAX_THREADS; i++)
2462 SitIdleEvent[i] = CreateEvent(0, FALSE, FALSE, 0);
2465 // Initialize splitPoints[] locks
2466 for (i = 0; i < MAX_THREADS; i++)
2467 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2468 lock_init(&(threads[i].splitPoints[j].lock));
2470 // Will be set just before program exits to properly end the threads
2471 AllThreadsShouldExit = false;
2473 // Threads will be put to sleep as soon as created
2474 AllThreadsShouldSleep = true;
2476 // All threads except the main thread should be initialized to THREAD_AVAILABLE
2478 threads[0].state = THREAD_SEARCHING;
2479 for (i = 1; i < MAX_THREADS; i++)
2480 threads[i].state = THREAD_AVAILABLE;
2482 // Launch the helper threads
2483 for (i = 1; i < MAX_THREADS; i++)
2486 #if !defined(_MSC_VER)
2487 ok = (pthread_create(pthread, NULL, init_thread, (void*)(&i)) == 0);
2489 ok = (CreateThread(NULL, 0, init_thread, (LPVOID)(&i), 0, NULL) != NULL);
2494 cout << "Failed to create thread number " << i << endl;
2495 Application::exit_with_failure();
2498 // Wait until the thread has finished launching and is gone to sleep
2499 while (threads[i].state != THREAD_SLEEPING) {}
2504 // exit_threads() is called when the program exits. It makes all the
2505 // helper threads exit cleanly.
2507 void ThreadsManager::exit_threads() {
2509 ActiveThreads = MAX_THREADS; // HACK
2510 AllThreadsShouldSleep = true; // HACK
2511 wake_sleeping_threads();
2513 // This makes the threads to exit idle_loop()
2514 AllThreadsShouldExit = true;
2516 // Wait for thread termination
2517 for (int i = 1; i < MAX_THREADS; i++)
2518 while (threads[i].state != THREAD_TERMINATED) {}
2520 // Now we can safely destroy the locks
2521 for (int i = 0; i < MAX_THREADS; i++)
2522 for (int j = 0; j < MAX_ACTIVE_SPLIT_POINTS; j++)
2523 lock_destroy(&(threads[i].splitPoints[j].lock));
2525 lock_destroy(&WaitLock);
2526 lock_destroy(&MPLock);
2530 // thread_should_stop() checks whether the thread should stop its search.
2531 // This can happen if a beta cutoff has occurred in the thread's currently
2532 // active split point, or in some ancestor of the current split point.
2534 bool ThreadsManager::thread_should_stop(int threadID) const {
2536 assert(threadID >= 0 && threadID < ActiveThreads);
2540 for (sp = threads[threadID].splitPoint; sp && !sp->stopRequest; sp = sp->parent) {}
2545 // thread_is_available() checks whether the thread with threadID "slave" is
2546 // available to help the thread with threadID "master" at a split point. An
2547 // obvious requirement is that "slave" must be idle. With more than two
2548 // threads, this is not by itself sufficient: If "slave" is the master of
2549 // some active split point, it is only available as a slave to the other
2550 // threads which are busy searching the split point at the top of "slave"'s
2551 // split point stack (the "helpful master concept" in YBWC terminology).
2553 bool ThreadsManager::thread_is_available(int slave, int master) const {
2555 assert(slave >= 0 && slave < ActiveThreads);
2556 assert(master >= 0 && master < ActiveThreads);
2557 assert(ActiveThreads > 1);
2559 if (threads[slave].state != THREAD_AVAILABLE || slave == master)
2562 // Make a local copy to be sure doesn't change under our feet
2563 int localActiveSplitPoints = threads[slave].activeSplitPoints;
2565 if (localActiveSplitPoints == 0)
2566 // No active split points means that the thread is available as
2567 // a slave for any other thread.
2570 if (ActiveThreads == 2)
2573 // Apply the "helpful master" concept if possible. Use localActiveSplitPoints
2574 // that is known to be > 0, instead of threads[slave].activeSplitPoints that
2575 // could have been set to 0 by another thread leading to an out of bound access.
2576 if (threads[slave].splitPoints[localActiveSplitPoints - 1].slaves[master])
2583 // available_thread_exists() tries to find an idle thread which is available as
2584 // a slave for the thread with threadID "master".
2586 bool ThreadsManager::available_thread_exists(int master) const {
2588 assert(master >= 0 && master < ActiveThreads);
2589 assert(ActiveThreads > 1);
2591 for (int i = 0; i < ActiveThreads; i++)
2592 if (thread_is_available(i, master))
2599 // split() does the actual work of distributing the work at a node between
2600 // several available threads. If it does not succeed in splitting the
2601 // node (because no idle threads are available, or because we have no unused
2602 // split point objects), the function immediately returns. If splitting is
2603 // possible, a SplitPoint object is initialized with all the data that must be
2604 // copied to the helper threads and we tell our helper threads that they have
2605 // been assigned work. This will cause them to instantly leave their idle loops
2606 // and call sp_search(). When all threads have returned from sp_search() then
2609 template <bool Fake>
2610 void ThreadsManager::split(const Position& p, SearchStack* ss, int ply, Value* alpha,
2611 const Value beta, Value* bestValue, Depth depth, Move threatMove,
2612 bool mateThreat, int* moveCount, MovePicker* mp, bool pvNode) {
2614 assert(ply > 0 && ply < PLY_MAX);
2615 assert(*bestValue >= -VALUE_INFINITE);
2616 assert(*bestValue <= *alpha);
2617 assert(*alpha < beta);
2618 assert(beta <= VALUE_INFINITE);
2619 assert(depth > Depth(0));
2620 assert(p.thread() >= 0 && p.thread() < ActiveThreads);
2621 assert(ActiveThreads > 1);
2623 int i, master = p.thread();
2624 Thread& masterThread = threads[master];
2628 // If no other thread is available to help us, or if we have too many
2629 // active split points, don't split.
2630 if ( !available_thread_exists(master)
2631 || masterThread.activeSplitPoints >= MAX_ACTIVE_SPLIT_POINTS)
2633 lock_release(&MPLock);
2637 // Pick the next available split point object from the split point stack
2638 SplitPoint& splitPoint = masterThread.splitPoints[masterThread.activeSplitPoints++];
2640 // Initialize the split point object
2641 splitPoint.parent = masterThread.splitPoint;
2642 splitPoint.stopRequest = false;
2643 splitPoint.ply = ply;
2644 splitPoint.depth = depth;
2645 splitPoint.threatMove = threatMove;
2646 splitPoint.mateThreat = mateThreat;
2647 splitPoint.alpha = *alpha;
2648 splitPoint.beta = beta;
2649 splitPoint.pvNode = pvNode;
2650 splitPoint.bestValue = *bestValue;
2652 splitPoint.moveCount = *moveCount;
2653 splitPoint.pos = &p;
2654 splitPoint.parentSstack = ss;
2655 for (i = 0; i < ActiveThreads; i++)
2656 splitPoint.slaves[i] = 0;
2658 masterThread.splitPoint = &splitPoint;
2660 // If we are here it means we are not available
2661 assert(masterThread.state != THREAD_AVAILABLE);
2663 int workersCnt = 1; // At least the master is included
2665 // Allocate available threads setting state to THREAD_BOOKED
2666 for (i = 0; !Fake && i < ActiveThreads && workersCnt < MaxThreadsPerSplitPoint; i++)
2667 if (thread_is_available(i, master))
2669 threads[i].state = THREAD_BOOKED;
2670 threads[i].splitPoint = &splitPoint;
2671 splitPoint.slaves[i] = 1;
2675 assert(Fake || workersCnt > 1);
2677 // We can release the lock because slave threads are already booked and master is not available
2678 lock_release(&MPLock);
2680 // Tell the threads that they have work to do. This will make them leave
2681 // their idle loop. But before copy search stack tail for each thread.
2682 for (i = 0; i < ActiveThreads; i++)
2683 if (i == master || splitPoint.slaves[i])
2685 memcpy(splitPoint.sstack[i], ss - 1, 4 * sizeof(SearchStack));
2687 assert(i == master || threads[i].state == THREAD_BOOKED);
2689 threads[i].state = THREAD_WORKISWAITING; // This makes the slave to exit from idle_loop()
2692 // Everything is set up. The master thread enters the idle loop, from
2693 // which it will instantly launch a search, because its state is
2694 // THREAD_WORKISWAITING. We send the split point as a second parameter to the
2695 // idle loop, which means that the main thread will return from the idle
2696 // loop when all threads have finished their work at this split point.
2697 idle_loop(master, &splitPoint);
2699 // We have returned from the idle loop, which means that all threads are
2700 // finished. Update alpha and bestValue, and return.
2703 *alpha = splitPoint.alpha;
2704 *bestValue = splitPoint.bestValue;
2705 masterThread.activeSplitPoints--;
2706 masterThread.splitPoint = splitPoint.parent;
2708 lock_release(&MPLock);
2712 // wake_sleeping_threads() wakes up all sleeping threads when it is time
2713 // to start a new search from the root.
2715 void ThreadsManager::wake_sleeping_threads() {
2717 assert(AllThreadsShouldSleep);
2718 assert(ActiveThreads > 0);
2720 AllThreadsShouldSleep = false;
2722 if (ActiveThreads == 1)
2725 #if !defined(_MSC_VER)
2726 pthread_mutex_lock(&WaitLock);
2727 pthread_cond_broadcast(&WaitCond);
2728 pthread_mutex_unlock(&WaitLock);
2730 for (int i = 1; i < MAX_THREADS; i++)
2731 SetEvent(SitIdleEvent[i]);
2737 // put_threads_to_sleep() makes all the threads go to sleep just before
2738 // to leave think(), at the end of the search. Threads should have already
2739 // finished the job and should be idle.
2741 void ThreadsManager::put_threads_to_sleep() {
2743 assert(!AllThreadsShouldSleep);
2745 // This makes the threads to go to sleep
2746 AllThreadsShouldSleep = true;
2749 /// The RootMoveList class
2751 // RootMoveList c'tor
2753 RootMoveList::RootMoveList(Position& pos, Move searchMoves[]) : count(0) {
2755 SearchStack ss[PLY_MAX_PLUS_2];
2756 MoveStack mlist[MaxRootMoves];
2758 bool includeAllMoves = (searchMoves[0] == MOVE_NONE);
2760 // Initialize search stack
2761 init_ss_array(ss, PLY_MAX_PLUS_2);
2762 ss[0].currentMove = ss[0].bestMove = MOVE_NONE;
2763 ss[0].eval = VALUE_NONE;
2765 // Generate all legal moves
2766 MoveStack* last = generate_moves(pos, mlist);
2768 // Add each move to the moves[] array
2769 for (MoveStack* cur = mlist; cur != last; cur++)
2771 bool includeMove = includeAllMoves;
2773 for (int k = 0; !includeMove && searchMoves[k] != MOVE_NONE; k++)
2774 includeMove = (searchMoves[k] == cur->move);
2779 // Find a quick score for the move
2780 pos.do_move(cur->move, st);
2781 ss[0].currentMove = cur->move;
2782 moves[count].move = cur->move;
2783 moves[count].score = -qsearch<PV>(pos, ss+1, -VALUE_INFINITE, VALUE_INFINITE, Depth(0), 1);
2784 moves[count].pv[0] = cur->move;
2785 moves[count].pv[1] = MOVE_NONE;
2786 pos.undo_move(cur->move);
2793 // RootMoveList simple methods definitions
2795 void RootMoveList::set_move_nodes(int moveNum, int64_t nodes) {
2797 moves[moveNum].nodes = nodes;
2798 moves[moveNum].cumulativeNodes += nodes;
2801 void RootMoveList::set_beta_counters(int moveNum, int64_t our, int64_t their) {
2803 moves[moveNum].ourBeta = our;
2804 moves[moveNum].theirBeta = their;
2807 void RootMoveList::set_move_pv(int moveNum, const Move pv[]) {
2811 for (j = 0; pv[j] != MOVE_NONE; j++)
2812 moves[moveNum].pv[j] = pv[j];
2814 moves[moveNum].pv[j] = MOVE_NONE;
2818 // RootMoveList::sort() sorts the root move list at the beginning of a new
2821 void RootMoveList::sort() {
2823 sort_multipv(count - 1); // Sort all items
2827 // RootMoveList::sort_multipv() sorts the first few moves in the root move
2828 // list by their scores and depths. It is used to order the different PVs
2829 // correctly in MultiPV mode.
2831 void RootMoveList::sort_multipv(int n) {
2835 for (i = 1; i <= n; i++)
2837 RootMove rm = moves[i];
2838 for (j = i; j > 0 && moves[j - 1] < rm; j--)
2839 moves[j] = moves[j - 1];